To determine a usage status of an electrical device, e.g., whether the electrical device is turned on or turned off, an additional component needs to be provided on an electrical appliance or mechanical device that consumes electrical power. In a conventional solution that uses an ammeter or a power measuring equipment, an existing power line needs to disconnected, and the ammeter or power measuring equipment is then connected in series thereto. However, the above method not only involves complex application details but also impairs an existing wire, hence resulting limitations for a user. Further, if a clamp meter is adopted, the clamp meter cannot be readily used in a two-wire application. In order to use the two-wire, the two-wire power line needs to be separated, which is equivalently decomposing the power line, in a way that user may be less willing to use such approach. There are some other methods having issues of high costs.